EFFECT OF THE SOLVENT COMPOSITION AND OF THE ADDITION OF 15-CROWN-5 ON THE CONDUCTANCE OF LITHIUM PICRATE AND LITHIUM PERCHLORATE IN ACETONITRILE PLUS NITROMETHANE MIXTURES

Conductivity data for lithium picrate and lithium perchlorate in aceto nitrile + nitromethane isodielectric mixtures at 25 degrees C are repo rted. Treatment of the data in terms of the Fuoss 1980 equation shows that the ion pair association of these electrolytes depends strongly o n the composition rather than on the macroscopic dielectric constant o f the solvent. Such a result has been rationalized in terms of specifi c ion-solvent interactions, related to the peculiar properties of the acetonitrile + nitromethane mixtures. The effect of the complexation o f lithium ion with 15 crown (15C5) on the ionization of both electroly tes was also investigated. The results show that the shielding of the electric field between the lithium ion and counterion, caused by the c rown ether, reduces drastically the ion pairing. The association const ants for each electrolyte in the ternary system acetonitrile + nitrome thane + 15C5 become, in addition, of the same order of magnitude in th e whole range of solvent composition, as expected for isodielectric so lvent mixtures.